:root {
  --background-color: #2c3e50;
  --border-color: #7591ad;
  --nav-background-color: #34495e;
  --text-color: #34495e;
}

* {
  margin: 0;
  padding: 0;
}

html {
  font-size: 14px;
}

body{
    width: 100vw;
    height: 100vh;
    background-color: var(--background-color);
    display: flex;
    justify-content: center;
    align-items: center;
    font-family: Shijie;
}

@font-face {
    font-family: "Shijie";
    src: url("../intro3S/汉仪正圆-45S.ttf");
  }

nav {
  position: relative;
  width: 550px;
  height: 50px;
  background-color: var(--nav-background-color);
  border-radius: 8px;
  box-shadow: 0 2px 3px rgba(0, 0, 0, 0.1);
}

nav a {
  position: relative;
  display: block;
  float: left;
  font-size: 15px;
  line-height: 50px;
  height: 50px;
  color: #fff;
  text-transform: uppercase;
  text-decoration: none;
  text-align: center;
  z-index: 10;
}

nav a:nth-child(1){
    width: 110px;
}
nav a:nth-child(2){
    width: 110px;
}
nav a:nth-child(3){
    width: 110px;
}
nav a:nth-child(4){
    width: 110px;
}
nav a:nth-child(5){
    width: 110px;
}

nav .animation{
    position: absolute;
    height: 100%;
    width: 110px;
    background-color: #ffa018;
    z-index: 9;
    border-radius: 8px;
    transition: all 0.2s;
}

.start-home,
nav a:nth-child(1):hover~.animation{
    width: 110px;
    left: 0px;
}
.start-about,
nav a:nth-child(2):hover~.animation{
    width: 110px;
    left: 110px;
}
.start-download,
nav a:nth-child(3):hover~.animation{
    width: 110px;
    left: 220px;
}
.start-contact,
nav a:nth-child(4):hover~.animation{
    width: 110px;
    left: 330px;
}
.start-login,
nav a:nth-child(5):hover~.animation{
    width: 110px;
    left: 440px;
}